In general, a variety of materials have been blended with soils to enhance or improve the properties thereof. In early highway construction, soil and rocks were mixed to provide a more stable, free draining, better performing roadbed. Lime has routinely been added to clay and silty soils to reduce their plasticities and to reduce their swelling potential. Portland cement has been added to several types of soils, being mixed in place or in a batch plant for achieving an improved highway base material. More recently, woven synthetic materials have been places in horizontal layers of soil in order to achieve steep, stable earth slopes.
Examples of the last technique, involving the use of so-called geotextiles, have been described in the patent literature. U.S. Pat. No. 3,934,421, for instance, is directed toward a matting of continuous thermoplastic filaments that are bonded together at intersections. When placed in loose soil, the matting provides increased vertical load bearing capacity and resistance to lateral deformation.
U.S. Pat. No. 4,002,034 also discloses a matting, anchored to the ground, for preventing erosion. The matting is a multi-layered composite providing an uppermost layer having the finest fibers and least pore spaces and a ground side layer having the thickest fibers and greatest pore spaces.
U.S. Pat. No. 4,329,392 provides a layered matting designed to inhibit rearrangement of soil particles. The matting comprises self-spun synthetic polymer filaments with macrofibers forming a web, a filter layer of finer fibers bonded thereto and an intermediate layer of other fibers therebetween. The mat has use below water level to control erosion.
U.S. Pat. No. 4,421,439 is directed toward woven fabric, comprising filaments such as polyester, polyamides and polyolefins. The fabric is positioned beneath sand, gravel, stones, clay, loam and the like at a depth of at least 10 cm. The invention is based on the particular construction of the fabric which gives it improved load bearing performance.
Another unique configuration geotextile material is disclosed in U.S. Pat. No. 4,472,086. The material is used as a reinforcement for the construction of roadways and on slopes and river banks to control erosion.
Despite the wide-spread use of man-made or synthetic filaments in fabrics, matting and the like as a reinforcement for soil, the foregoing patents have not taught the use of individual fiber blended with the soil.
U.S. Pat. Nos. 4,790,691 and 4,867,614, however, do teach the addition of individual fibers or bundles or discrete synthetic textile materials, as opposed to textile fabrics, which are blended with all forms of soil to improve the engineering properties of the soil. Practice of these patents facilitates construction at roadways, highways, building sites, parking areas and the like by stabilizing the soil and improving the load bearing capabilities thereof.
U.S. Pat. No. 4,819,933, similarly discloses the use of a mixture comprising sand and individual strands of synthetic fibers to produce a relatively soft, non-grassed, playing surface for equestrian and sports events.
Nevertheless, no one has previously punched textile fibers directly into soil. Consequently, improving the appearance and playing characteristics of turfed surfaces in this manner appears not to have been investigated heretofore.